The present invention relates to giant magnetoresitive (GMR) devices and more particularly to means for stabilizing GMR devices.
The edges of a GMR stack must be stabilized to ensure that the magnetization of the edges does not rotate when exposed to an applied field. If the magnetization at the edges of a GMR stack moves during operation, this leads to noise which makes data recovery difficult or impossible. Previously, an oxidation process was used to provide stability. During the oxidation process, material near the edges of a GMR stack is transformed into an oxide, which helps to maintain the stability of the device. The result of oxidizing the material at the device edges appears to be an increase in the coercivity of these regions. The oxide may include some antiferromagnetic components that couple with the device edges, thereby pinning the magnetization of the device edges in a single direction. Additional steps are also typically performed during the oxidation process such as annealing. The annealing may be performed in the presence of a field.
U.S. Pat. No. 5,756,366, entitled xe2x80x9cMAGNETIC HARDENING OF BIT EDGES OF MAGNETORESISTIVE RAMxe2x80x9d (the ""366 patent) describes oxidation of device edges in a magnetoresitive RAM. The ""366 patent discloses that the edges 23 of magnetic layers 20xe2x80x2 and 24xe2x80x2 are cleaned and then oxidized by placing the wafer in an oxygen plasma for a length of time. Several hundred to a thousand angstroms of magnetic material are oxidized as shown by the cross-hatched portions 25 shown in FIG. 6 of the ""366 patent. The cross-hatched edge portions 25 are magnetically harder than the inner portion of magnetic layers 20xe2x80x2 and 24xe2x80x2. The higher coercivity level of oxidized edge portions 25 acts to prevent bit edge reversal in the final magnetoresistive RAM device.
The prior art, therefore, discloses the transformation of the material at the edges of a device. The prior art does not disclose the deposition of additional layers on the device edges to provide stability. Such additional layers are desirable because they couple strongly with the device edges, and help to ensure that the device""s edges do not rotate in the presence of an external field.
A stabilized GMR device according to the present invention includes a GMR stack having a first and a second edge. Stabilization means are positioned adjacent to the first and the second edge of the GMR stack for stabilizing the GMR stack. The GMR stack includes a first layer of ferromagnetic material and a second layer of ferromagnetic material. A spacer layer is positioned between the first and the second ferromagnetic layers. A buffer layer is positioned adjacent to the first magnetic layer and a cap layer is positioned adjacent to the second ferromagnetic layer. The stabilization means include a first coupler layer positioned adjacent to the first edge of the GMR stack and a second coupler layer positioned adjacent to the second edge of the GMR stack. The stabilization means also include a first ferromagnetic layer positioned adjacent to the first coupler layer and a second ferromagnetic layer positioned adjacent to the second coupler layer.
The stabilization means couples strongly anti-parallel to the ferromagnetic layers of the GMR stack, thereby effectively xe2x80x9chardeningxe2x80x9d the edges of the GMR stack, and making them less susceptible to reversal in an applied field. The stabilization means may be used to stabilize folded VGMR read heads, single VGMR read heads, GMR MRAM devices or other similar devices.